Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C67/00—Preparation of carboxylic acid esters
  • C07C67/30—Preparation of carboxylic acid esters by modifying the acid moiety of the ester, such modification not being an introduction of an ester group
  • C07C67/313—Preparation of carboxylic acid esters by modifying the acid moiety of the ester, such modification not being an introduction of an ester group by introduction of doubly bound oxygen containing functional groups, e.g. carboxyl groups

Definitions

• the present invention relates to a process for producing a glyoxylic acid ester by catalytic oxydehydrogenation of the corresponding glycolic acid ester in the gas phase.
• glycolic acid esters can be oxydehydrogenated on heterogeneous catalysts in the gas phase to form glyoxylic acid esters.
• the presence of the water of reaction causes at least partial saponification of the glycolic acid esters and glyoxylic acid esters to give acids and alcohols. This reaction takes place in particular in the condensed phase.
• the hydrate, the hemiacetal and the acetal of the respective glyoxylic acid ester are formed directly during the condensation of the reaction mixture.
• the present invention therefore provides a process for the preparation of a glyoxylic acid ester by kata - lytic oxydehydrogenation of the corresponding Glykolklareesters in the gas phase, characterized in that the gaseous reaction mixture formed in the oxydehydrogenation is conducted by dosing of an entraining agent in the central part of a fractionating column, wherein the reaction mixture cools rapidly and the water of reaction and other low boilers are distilled off together with the entraining agent overhead and the glyoxylic acid ester is obtained as the bottom product.
• glycolic acid esters of the general formula HO-CH 2 -COOR are used in vapor form.
• R is a hydrocarbon radical, preferably an aliphatic, straight-chain or branched alkyl radical with 1 to 8 C atoms, in particular with 1 to 5 C atoms.
• the gaseous glycolic acid esters are passed over the catalyst together with oxygen or an oxygen-containing gas such as air. It is preferably diluted with a carrier gas such as nitrogen or noble gases.
• any oxydehydrogenation catalyst can be used as a catalyst for the process according to the invention.
• the catalyst preferably contains at least one of the elements V, Au, Mo, Ag, Cu, Sn, Sb, Bi and P.
• other elements of the 3rd to 5th main group also have a catalytic effect.
• the elements mentioned are either in metallic form or in the form of their compounds, e.g. introduced into the reaction zone as oxides, nitrates, acetates, acetylacetonates, oxalates, citrates or halides.
• the catalytically active elements are preferably applied to support materials.
• Silicates, aluminum oxides, aluminum silicates, pumice or coal are particularly suitable as carriers.
• Silicates, aluminum oxides or aluminum silicates are preferably used.
• Aluminum silicates with a BET surface area of less than 50 m 2 / g are particularly advantageous.
• the total amount of elements on the carrier can vary within wide limits. In general, it is 0.01 to 50 wt .-%, preferably 0.1 to 20 wt .-%, based on the total mass of the supported catalyst.
• the catalytically active components are expediently brought to the support in the form of a solution, then the solvent is evaporated off and the catalyst is dried. Water, hydrochloric acid, nitric acid, alkali solutions or aqueous ammonia solution, preferably water and hydrochloric acid, are generally used as solvents.
• the active components can also be used without a carrier.
• the oxidative dehydrogenation is preferably carried out generally at temperatures between 100 and 600 ° C, between 200 and 400 0 C.
• the residence time is preferably between 0.1 and 10 seconds, but in particular between 0.1 and 1 second. Satisfactory results are still obtained even outside these limits.
• Oxydehydrogenation is preferably carried out at normal pressure, but reduced or increased pressures can also be used, i.e. 0.01 to 100 bar.
• the procedure is such that the glycolic acid ester and oxygen or oxygen-containing gas, and optionally the carrier gas, are fed from metering devices into an evaporation zone and the resulting gas mixture is then passed through a reaction tube which is heated from the outside and filled with the catalyst. It has proven advantageous to heat the oxygen or the oxygen-containing gas and the carrier gas to the reaction temperature before they are introduced into the evaporation zone.
• the gaseous reaction mixture is quenched (quenched) with an entrainer immediately after leaving the reactor and passed directly into the middle part of a fractionation column.
• the top product of the column contains the water and the alcohol formed as a by-product, as well as small amounts of other by-products such as formaldehyde and formic acid ester.
• the sump consists essentially of the glyoxylic acid ester and possibly unreacted glycolic acid ester; the glyoxylic acid ester can be separated from this mixture by conventional distillation.
• the entrainer can then be extracted from the top product by known methods, e.g. obtained by distillation or by phase separation and recycled.
• entrainer all substances which form azeotropes with water and alcohols are suitable as entrainer.
• a water-immiscible entrainer is preferred because this can then be separated off and returned as a separate phase after the condensation of the top product.
• the boiling point of the entrainer is preferably below the boiling point of the particular glyoxylic acid ester. However, at least the boiling point of the azeotrope must be below the boiling point of the glyoxylic acid ester.
• Suitable entraining agents are aliphatic and aromatic hydrocarbons, which may contain heteroatoms, such as CH 2 Cl 2 , CHCl 3 , CC14, n-pentane, n-hexane, cyclohexane, nonane, diisopropyl ether, methyl ethyl ketone, benzene and toluene, especially n-pentane and Cyclohexane.
• glyoxylic acid esters are valuable starting and intermediate products for a number of syntheses of pharmaceutically active compounds, e.g. Allantoin, substituted glycine or alkaloids (such as tetrahydroisoquinoline alkaloids).
• An aluminum silicate with a BET surface area of 1 m 2 g -1 is used as a support for the catalyst.
• the catalyst contains 7.8% by weight of Ag and 3.7% by weight of V.
• 2.0 g of vanadium pentoxide is dissolved in 15 ml of concentrated hydrochloric acid, 30 g of catalyst support are soaked in this solution and the solvent is evaporated the steam bath.
• 3.7 g of silver nitrate are applied after dissolving in 6 ml of water.
• the catalyst is then dried at 110 ° C.
• 7.5 ml of this catalyst are in a vertically arranged glass reactor 150 mm long and 20 mm in diameter was filled and heated in a gas stream of 45 mmol / h oxygen and 2.5 mol / h nitrogen at 400 ° C. for three hours.
• the reactor is heated from the outside and the temperature inside is measured using a thermocouple.
• test After a start-up time of 1 hour to set constant operating conditions, the test is continued over a period of 4 hours.
• the gaseous reaction products are quenched with 150 ml / h of n-pentane as entrainer and passed into the middle section of a fractionation column (length: 600 mm, diameter: 55 mm, filling: Braunschweig Wendeln).
• the column temperature is 70 ° C in the upper part and 90 ° C in the lower part.
• a 2-phase condensate is obtained at the top of the column.
• 5.6 g of aqueous phase are produced with the composition:
• the bottom product consists predominantly of methyl glyoxylate (17.0 g), corresponding to a yield of 74.5%, based on the glycolic acid methyl ester used.
• Example 2 Analogously to Example 1, 6 ml / h of n-butyl glycolate (46.3 mmol / h), 44.6 mmol / h of oxygen and 2.5 mol / h of nitrogen are introduced into the apparatus described there.
• the reactor is filled with 15 ml of a supported aluminum silicate catalyst which contains 8.05% by weight of Bi and 1.95% by weight of V on a support as in Example 1.
• the reaction temperature is 250 ° C.
• reaction products are quenched with 20 ml / h of cyclohexane as entrainer and passed into the middle part of the column.
• the column temperature is 95 ° C in the upper part and 100 ° C in the lower part.
• a 2-phase condensate is obtained at the top of the column.
• the bottom product contains 10.3 g of n-butyl glyoxylate, corresponding to a yield of 42.1%, based on the n-butyl glycolate used.

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Citations (2)

• 1983
  • 1983-06-29 DE DE3323372A patent/DE3323372A1/de not_active Withdrawn
• 1984
  • 1984-06-26 AT AT84107326T patent/ATE18759T1/de not_active IP Right Cessation
  • 1984-06-26 EP EP84107326A patent/EP0130533B1/fr not_active Expired
  • 1984-06-26 DE DE8484107326T patent/DE3460060D1/de not_active Expired
  • 1984-06-28 ZA ZA844935A patent/ZA844935B/xx unknown
  • 1984-06-28 JP JP59132145A patent/JPS6023345A/ja active Pending
  • 1984-06-28 AU AU30007/84A patent/AU560545B2/en not_active Ceased
  • 1984-06-28 CA CA000457786A patent/CA1224216A/fr not_active Expired

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